Flexible electric heating element



Patented Mar. 2, 1954 Zeman UNITED STATES PATENT orFlcE 19 Claims.

The invention relates to flexible electric heating elements and their application to condensation apparatus, fractionating apparatus, pipes and other apparatus especially condensation and fractionating apparatus of the electrically heated column type.

In column heating, condensation may take place at a stage earlier than desired. It is, therefore, necessary sometimes to apply heat to different parts of, say, a fractionating column. Indeed the problems presented in heating comparatively high temperature apparatus for instance fractionating columns, chemical asks and pipes in chemical laboratories are manifold particularly due to the large variety of sizes in use. Column diameters vary from l" to 8" and length variations are in proportion. Furthermore, on occasion only parts of a setup require application of heat. The most convenient method of applying heat is by means of electricity, both because of ease of control and also because of the temperatures which can readily be attained.

At present it is usual practice when attempting to heat by means of electricity to use spiral bare or insulated resistance wire Wound helically direct on the tube and to surround the heating element With layers of heat insulating materials to prevent losses. Heating pads made incertain shapes have been used. They are, however, difficult to keep in position, and a large number of them may be required.

The invention has for its object to provide an improved flexible electric heating element suitable for attaching to fabrics or other surfaces in a very convenient Way, and as a secondary object to apply such elements to apparatus as refer-red to above and to overcome the aforesaid disadvantages.

The invention consists in a flexible electric heating element comprising a long mechanically and electrically continuous strip, the central part of which is made of a ribbon or band of resistance Wire so fabricated as to be extensible both in the direction of length and also in the direction of Width, which central part is provided on each edge with a border made of an insulating fiber attached to the aforesaid resistance wire and also capable of extension, both in the direction of length and also Width.

The invention also consists in flexible electric heating elements in accordance with the preceding paragraph having one or more ofthe following additional features, namely:

(a) The band of resistance wire is' made by knitting, particularly warp knitting;

(b) The border is made by knitting, particularly warp knitting;

(c) Both band of resistance Wire and border are fabricated into the iiexible electric heating element simultaneously;

(d) The flexible electric heating element is made in a continuous strip as stated and may then be cut into lengths and attached in any suitable Way to fabric or any other article for low temperature heating thereof.

The invention also consists in a composite ilexible electric heating element formed from an elastic base of insulating tape to the surface of which is attached a flexible electric heating element formed in accordance with either of the preceding two paragraphs.

The invention also consists in a composite flexible electric heating element formed from a length of nexible and elastic insulating hose, tape or the like produced of preferably knitted or woven glass bers on which is mounted or secured a flexible electric heating element, in accordance with any of the preceding three paragraphs.

The invention also consists in flexible electric heating elements in accordance with any of the preceding four paragraphs in which to prevent heat from escaping outward, heat insulating material is mounted on the flexible electric heating element, in addition to which if desired a protecting covering is applied for instance to the edge if a tape be used for holding the insulating material in position, also in such a Way that it does not interfere with the elastic properties of the supporting tape.

The invention also consists in iiexible electric heating elements manufactured substantially as herein described.

The invention also consists in flexible electric heating elements in accordance with any of the preceding six paragraphs applied to apparatus which may be heated to a comparatively high temperature for instance condensation apparatus, fractionating apparatus, chemical iiasks or pipes used in chemical laboratories especially condensation and fractions-ting apparatus of the column type, and more particularly electrically heated column heaters.

The invention also consists in an alternative to the prece-ding paragraph namely in which the Referring to the accompanying diagrammatic drawings:

Figure 1 illustrates a Warp knitted flexible electric heating element according to one form of the present invention comprising a middle section of wire and other selvedges of insulating material;

Figure 2 illustrates a Warp knitted base of insulating material to which the flexible electric heating element of Figure 1 may be aiixed.

Figure 3 illustrates a flexible electric heating element embodying the invention and or 2-ply construction; Figure 4 illustrates a further modied form of a eXible electric heating element embodying the invention and of 3-ply construction.

In carrying the invention into eifect in the form shown by way of example in Figure l, resistance wires or strands a of suitably thin gauge and fiber glass threads or strands b are Warp knitted together on a suitable knitting machine, for example a pyjama girdle knitting machine. As indicated in the drawings and as generally known in the knitting art, a warp knitted fabric includes plural strands and the direction of knitting of the strands is longitudinal, that is lengthwise of the fabric being produced. The machine is arranged to continuously knit the resistance Wire as a central ribbon or band c including a plurality of strands, and the fiber glass to form opposite borders d again including a piurality of strands on each edge of band c, for which purpose the usual tassel arrangement of the knitting machine is put out of action. The tension of the machine should be adjusted to suit the metal being knitted, and the fiber glass for the borders. In this Way a continuous warp knitted strip of exible electric heating eiement is provided which can be cut into any desired vlength and used, for instance, for attachment to fabric of any kind including gloves, by stitching, by crimping, by stapling, or by adhesive means, or in any other suitable way, the idea being that the border holds the'resistance Wires in position with respect to the part to which the heater is attached.

A suitable base is illustrated in Figure 2, comprising a warp knitted web e made in a similar manner to the resistance web of Figure l so that it is constructed entirely of fiber glass thread. It may be of the same width as the web of Figw ure 1, or a greater width, or even a somewhat lesser width.

In Ithis way, either in accordance with Figure l or in accordance with Figure 1 and Figure 2 com bined is provided a low temperature heater, suitable for use for heating, for instance, blankets, garments, clothing, bedwarmers and domestic flasks or vessels. It may also be used for the purpose of heating to higher Atenlperatures for instance for column heating, In the last inentioned case, and indeed for other processes using say a combination of Figure 1 and Figure 2, the attachment of webs according to the -two igures should preferably be made in such a way as not to destroy substantially the iexibility, vfor instance, the attachment being made by stitching in loop form.

Figure 3 illustrates a eXible electric heating element comprising an elongated unitary'knitted fabric strip of Z-ply construction vthat is extensible both in the direction of its Ywidth and its length. The stri-p having in one ply at least three distinct knitted adjacent areas respectively co extensive in length with the length of the strip and respectively defining a central portion conportion of conducting strands a".

fi sisting substantially solely of knitted electrical conducted strands a and opposite border portions consisting substantially solely of knitted insulating strands b', particularly glass strands. The second ply or second fabric strip embodies a warp knitted area or web e of insulating strands, particularly ber glass strands connected to the first mentioned fabric strip to provide the 2-ply construction of the heating element. This second fabric strip of glass strands is broken away in the drawing, but it is to be pointed out that it can be at least co-extensive in length and width with the other strip which embodies the central area of conducting strands and the border areas of insulating strands. As indicated in the drawing, both strips or plys in the arrangement of Figure 2 are warp knitted.

Figure 4 illustrates a further form of the invention similar to Figure 3 but with an added ply so that `Figure 4 illustrates a B-ply construction in which there is a rst layer of warp knitted insulating strands such as glass strands e, an intermediate layer consisting of border portions of insulating strands b", and a central area or This intermediate layer has secured to its opposite face another or third strip of insulating material such yas fiber vglass strands e" secured thereto.

Flexible electric heating elements as described may be made in standard lengths and one or more sed in combination as required. `llfhere more than one are used they are connected in parallel electrically. They may be wound under slight tension around a column and thus remain in position without further fixing; the top and bottom ends can be secured by suitable means for example by a ring of `closed coiled spring wire slipped over the tube.

Fibre glass is a particularly convenient material for the elastic base tape, but either for base or border may be replaced by any 4other suitable insulating material, knitted or woven in such ways as give elasticity.

It is therefore clear that the invention, as illustrated in the drawing, as provided by the warp knitting arrangement produces a tape or fabric strip that is iiexible in both the direction of its length and its width so as to provide a fabric that is both flexible and elastic withparticular reference to the disclosure of Figure 1. Woven material in contradistinction `to applicants arrangement, while being flexible, is not kelastic and a purl knit or circular knit arrangement possesses serious disadvantages in view of the fact that, in regard to utilization of the fabric as a heating element, the several courses in such knitted type fabrics include a single strand from beginning to end and in any event cannot provide an arrangement in which a central area in the longitudinal direction of the fabric strip -is rcomposed of a plurality of individual conducting strands which may be electrically connected in parallel.

I claim:

1. A flexible electric heating elementr compris ing a 'knitted fabric Vextensible both in the direction of its length and its width and having a area dedned by at least one inter-knitted no1 inflammable insulating strand, an adjacent second area deiined by .a plurality of inten knitted individual conducting strands, and a `third area denn-ed `by at least one inter-knitted non inammable insulating strand, said third area being immediately adjacent said second .area and the conducting strand cn opposite sides of the said second area being inter-knitted with the adjacent insulating strands in the respective first and third areas.

2. A flexible electric heating element as defined in and by claim 1, wherein said non-inflammable strands are glass and said conducting strand is resistance wire.

3. A fiexible electric heating element comprising an elongated unitary knitted fabric strip extensible both in the direction of its width and its length, said strip having at least three distinct knitted adjacent areas therein, said areas being co-extensive in length with the length of the strip and respectively defining a central portion and opposite border portions each of the border portions consisting substantially solely of knitted insulating strands and the fabric of the central portion consisting substantially solely of knitted electrically conducting strands.

4. A flexible electric heating element as defined in and by claim 3, in which said border portions comprise glass strands and said conductive portion comprises resistance wire strands.

5. A flexible electric heating element as defined in and by claim 3, and including a second fabric strip consisting solely of inter-connected strands of insulating material connected to one face of said first-mentioned strip as a protective insulating layer.

6. A heating element consisting of a fabric strip embodying adjacent areas comprising a first area of insulating strands, a second Warp knitted area of a plurality of strands cf resistance wire extensible both in the direction of its length and its width, and a third area of insulating Y strands, the said first and third areas being located on either side of and inter-connected with said second area.

7. A fiexible electric heating element extensible both in the direction of its length and its width consisting of a knitted fabric strip embodying adjacent inter-knitted areas comprising a first knitted area of insulating strands, a second Warpknitted area of a plurality of strands of resistance wire, and a third knitted area of insulating strands, the said first and third areas being located on either side of said second area.

8. A flexible electric heating element extensible both in the direction of its length and its width consisting of a warp knitted fabric strip embodying adjacent inter-knitted areas comprising a first warp-knitted area of insulating strands, a second warp-knitted area of resistance wire, and a third warp-knitted area of insulating strands, the said first and third areas being located on either side of said second area.

9. A flexible electric heating element as defined in and by claim 3, in which said insulating strands are glass strands.

l0. A flexible electric heating element as defined in and by claim 9 and a second fabric strip embodying a warp-knitted area of insulating strands connected to one face of said first-mentioned fabric to define a two-ply heating element.

11. A fiexible electric heating element as defined in and by claim 10, in which said second fabric strip is at least co-extensive in length and Width with said first-mentioned strip.

12. A knitted fabric strip comprising three discrete areas extending longitudinally of the strip, each area including a plurality of strands of the same material, one of said areas constituting a central area along the longitudinal axis of the strip, and the strands of the central area being of wire and insulating material constituting the strands of the other two areas and all said areas being Warp knitted.

13. A Warp knitted fabric strip embodying adjacent inter-knitted areas comprising a first warp knitted area of glass strands, a second warp knitted area of wire strands, and a third warp knitted area of glass strands, the said first and third areas being located on either side of said second area and each area embodying a plurality of individual strands extending lengthwise of the strip.

14. A flexible electric heating element comprising a knitted fabric extensible both in the direction of its length and its width and having a first area defined by at least one inter-knitted insulating strand, an adjacent second area defined by at least one inter-knitted conducting strand, and a third area defined by at least one inter-knitted insulating strand, said third area being immediately adjacent said second area and the conducting strand on opposite sides of the said second area being inter-knitted with the adjacent insulating strands in the respective first and third areas, and all said areas being co-extensive in length with the length of the strip.

l5. A fiexible electric heating element as defined in and by claim 3 including a second strip consisting solely of insulating material connected to one face of said first mentioned strip as a protective insulating layer.

16. A fiexible elecrtic heating element as defined in and by claim 15 and further including a third strip consisting solely of insulating material connected to the opposite face of said first mentioned strip.

17. A flexible electric heating element as defined in and by claim 16 in which both said second and third strip constitute fabric strips consisting of interconnected strands of insulating material.

18. A flexible electric heating element as defined in and by claim 8 and a second strip consisting solely of insulating material connected to one face of said first mentioned strip.

19. A fiexible electric heating element as defined in and by claim 18 and further including a third strip consisting solely of insulating material connected to the opposite face of said first mentioned strip.

HENRY HERBERT GOLDSTAUB.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 975,359 Hefter Nov. 8, 1910 1,234,927 Myers et al July 31, 1917 1,553,461 Negromanti Sept. 15, 1925 1,593,359 Randolph July 20, 1926 1,965,542 Colvin July 3, 1934 2,078,050 Beniston Apr. 20, 1937 2,307,231 Neff Jan. 5, 1943 2,372,673 Jacob Apr. 3, 1945 2,396,099 Hartwell Mar. 5, 1946 2,511,540 Osterheld June 13, 1950 FOREIGN PATENTS Number Country Date 205,314 Great Britain Oct. 18, 1923 

